DE102023101914A1 - Device and method for producing plastic parts from a mixture of pure plastic material and plastic recyclate - Google Patents

Abstract

A device (1) for producing plastic parts (2) from a mixture of pure plastic material (3) and plastic recyclate (4) as raw materials is presented, which comprises a plasticizing unit or an extruder (5) with a housing cylinder (7) equipped with a heating device (6), in which an extruder screw (8) coupled to a drive is rotatably mounted, wherein an inlet (9) serves to feed the raw materials (3, 4) to be processed into the housing cylinder (7) and at least one spray nozzle (10) for discharging a liquid melt stream (11) is present at the end of the extruder screw (8).The invention is characterized in that the device (1) has, in addition to the first extruder (5) processing the pure plastic material (3), at least one further extruder (12) used exclusively for processing the plastic recyclate (4).Furthermore, a method for producing plastic parts from a mixture of Pure plastic material (3) and plastic recyclate (4) as basic materials, with such a device (1) described.

Description

The invention relates to a device for producing plastic parts from a mixture of pure plastic material and recycled plastic and to a method suitable for this purpose.

A fundamental aim is increasingly to reuse plastics that have been produced and used, which is done, among other things, to save valuable resources. To do this, the basic materials, i.e. a pure plastic material and a recycled plastic, i.e. a plastic recyclate, must be mixed and then processed, i.e. melted, for example in an extruder or generally in a plasticizing unit, such as those used primarily for injection molding, whereby the extruder and the plasticizing unit are always considered synonymous in the following explanations. When processing plastic recyclates, for example, the problem arises that such recycled materials or recyclates often have or contain impurities that are detrimental to the production of a pure plastic with high usable quality. Another disadvantage of processing the recyclates is that they are in shredded form, but the components can have different sizes. Due to the different sized particles, the melting process requires special attention in order to produce a homogeneous melt of the liquid plastic. Both problems have so far led to relatively few recyclates being used in the production of plastics in practice, and thus the recycling rate is very low. This is also due to the fact that the quality requirements for the plastics produced are very high.

Extruders for the production of plastic parts are known in a wide variety of designs. They generally have a heating device that is used to melt the raw materials to be processed in a housing cylinder. An extruder screw coupled to a drive is rotatably mounted in the housing cylinder, with an inlet being used to feed the raw materials to be processed into the housing cylinder and at least one spray nozzle at the end of the extruder screw for discharging the liquid plastic melt stream. The raw materials, which are usually granules or powder, are compressed in the extruder and preheated using the heating device. In the subsequent conversion zone of the extruder, a molding compound or melt or melt stream is produced from the raw material. The material to be processed is then homogenized in the so-called discharge zone, compressed and expelled from the extruder at the temperature generated in the extruder.

The invention is based on the object of creating a device which overcomes the aforementioned disadvantages of the prior art and makes it possible to increase the proportion of recyclates used in the production of plastic parts from a mixture of pure plastic material and plastic recyclate. A suitable method is also to be specified for this purpose.

The invention solves this problem with the features of independent patent claims 1 and 13. Further embodiments of the invention are the subject of the respective subsequent subclaims.

A device for producing plastic parts from a mixture of pure plastic material and plastic recyclate as raw materials, comprising an extruder with a housing cylinder equipped with a heating device, in which an extruder screw coupled to a drive is rotatably mounted, wherein an inlet serves to feed the raw materials to be processed into the housing cylinder and at least one spray nozzle for discharging a liquid melt stream is present at the end of the extruder screw, was further developed according to the invention in such a way that the device, in addition to the first extruder which processes exclusively the pure plastic material, has at least one further extruder which is used exclusively for processing the plastic recyclate.

Until now, both the pure plastic material and the plastic recyclate were introduced into an extruder together and melted there. This procedure led to considerable problems in quality assurance, since for the reasons mentioned above, the plastic recyclates are often not as easy to process as a pure plastic material. The invention now takes a completely new approach, which consists in no longer using just one extruder in a device for producing plastic parts, but a second extruder, so that one extruder is used exclusively for processing the pure plastic material and another extruder is used exclusively for processing the plastic recyclate. After the melt stream generated in the extruder has been discharged, these are combined according to the invention to form a uniform melt stream, so that a very homogeneous plastic mixture is created that also meets high quality requirements. The invention therefore enables an individual plasticization decoration of the polymer melts from both basic materials.

In order to simplify the construction of the entire device, a first embodiment of the invention is that the extruders are of identical design. However, due to the different properties of the raw materials used, it is sensible, regardless of the identical design of the extruders used, to separately monitor and control, for example, the speed, the pressure of the extruder screw and/or the temperature within the extruder.

By using at least two independent extruders for processing the individual raw materials, it is necessary to combine the melt streams of the plastic produced in the respective extruder. For this purpose, a further proposal of the invention is to combine the melt streams of both extruders in a mixing device to form a mixed melt stream. The combination can take place outside the extruders, whereby an alternative embodiment can be seen in that both extruders are components of a mixing device in which the melt streams of the extruders are combined to form a mixed melt stream. Both solutions are therefore within the scope of the invention.

A particularly advantageous further development of the invention is that a measuring device for analyzing the properties of the mixed melt stream produced is present in the mixing device or the mixing device following the flow direction of the melt stream. The measuring device is preferably arranged after the mixing device so that the melt stream produced from both basic materials is subjected to a permanent measurement or a measurement carried out at defined time intervals. The measurement results generated in this way can be used directly to make statements about the quality of the plastic produced. These in turn allow intervention in the process, for example to eliminate disruptive influences. This measure therefore achieves a consistent quality of the plastic produced and the resulting waste is significantly reduced or completely avoided. For example, adjustments to the mixing ratio of the basic materials can be made based on the measurement results obtained.

In addition, it is of course also possible to use the measuring device for analyzing the properties of the melt streams on each of the melt streams emitted by the extruders, i.e. before they are combined in the mixing device. This means that the process can be influenced at an earlier point in time and, for example, the presence of impurities in one of the melt streams can be detected earlier.

A spectral-optical analysis measuring device has proven to be a suitable measuring device, although other analysis measuring devices can of course also be used. This generates an optical signal which, after being converted into an electrical signal, can be used and processed, for example, by means of an electronic processing unit.

Infrared light is preferably used to generate the optical signal. Due to the high intensity and quality of the light signal generated, a laser can of course also be used to generate the light required for the measurement in a spectral-optical analysis measuring device used according to the invention. Very precise measurement results can be achieved with the help of the infrared light signal or the laser light signal.

In order to be able to regulate or control the processes described above, it is advantageous according to one embodiment of the invention if the light signal from the measuring device is processed and evaluated by means of an electronic processing unit and a spectrometer. The electronic processing unit can therefore be used for several purposes according to the invention.

Thus, according to an advantageous development of the invention, the electronic processing unit and the measuring device are essential components of a control or regulation for adjusting the composition of the mixed melt flow. If an error signal of the plastic melt flow is sensed by the measuring device, the signal is compared with stored target values within the electronic processing unit and, in the event of deviations, the process is intervened in via a control system and, for example, the mixing ratio between the basic materials is changed, the temperature within the extruder or the pressure or the speed of the extruder screw is adjusted.

According to an advantageous embodiment of the device, the melt streams produced by the extruder are homogenized in a static mixer. The static mixer is arranged upstream of the measuring device and downstream of the mixing device.

A very advantageous embodiment of the invention is furthermore to be seen in the fact that the extruders are decoupled from one another, for which purpose the melt streams each pass through a valve, preferably a one-way valve, so that the melt streams can be switched on or off individually.

• -Einbringung je eines Grundstoffes über den Einlass in je einen der den jeweiligen Grundstoffen zugeordneten Extruder,
• -Aufschmelzen der Grundstoffe zu einem pastösen oder flüssigen Kunststoff,
• -Zusammenführung der einzelnen Schmelzeströme der Extruder zu einem Mischschmelzestrom,
• -Abführung des homogenen Mischschmelzestromes in einen die Negativform des herzustellenden Kunststoffteils aufweisenden Hohlraumes eines Spritzgusswerkzeuges.

The method according to the invention for producing plastic parts from a mixture of pure plastic material and plastic recyclate as basic materials, using a device described above, is characterized by the following process steps:

• -Introduction of one raw material each via the inlet into one of the extruders assigned to the respective raw materials,
• -Melting the raw materials to form a pasty or liquid plastic,
• -Combining the individual melt streams of the extruders into a mixed melt stream,
• -Discharge of the homogeneous mixed melt flow into a cavity of an injection molding tool containing the negative shape of the plastic part to be produced.

The method according to the invention enables the production of high-quality plastics from mixtures of pure plastic materials and plastic recyclates using the device described above, so that the proportion of plastic recyclates in the end products can be significantly increased, which in turn leads to a saving of valuable resources. The separate processing of the basic materials in individual extruders also enables optimal control of the melting process and the generation of the mixed melt stream.

According to a first embodiment of the method according to the invention, it is proposed that the mixed melt stream be examined for its composition using an analysis measuring device either permanently or at defined intervals. A spectral-optical analysis measuring device has proven to be particularly advantageous. As already described in detail in connection with the discussion of the device, any quality deviations that may occur can be addressed very flexibly and at short notice in this way.

According to a further development of the invention, the examination of the mixed melt stream leads, depending on the measurement result of the spectral-optical analysis measuring device by means of a comparison with target values stored in the electronic processing unit, including the electronic processing unit, to the possibility of implementing a control or regulation for adjusting the composition of the mixed melt stream by controlling the individual extruders and thus adjusting the consistency of the mixed melt stream to the desired quality requirements.

The invention is explained in more detail below with reference to the attached drawing. The embodiment shown does not represent a restriction to the variant shown, but merely serves to explain a principle of the invention. Identical or similar components are always designated with the same reference numerals. In order to be able to illustrate the functionality of the invention, the figures only show highly simplified schematic diagrams in which the components that are not essential to the invention have been omitted. However, this does not mean that such components are not present in a solution according to the invention.

The figure shows a device 1 for producing plastic parts 2 in an injection molding tool 18, in which at least two different basic materials 3 and 4 are used. The basic materials 3 and 4 are, on the one hand, a pure plastic material 3 and, on the other hand, a plastic recyclate 4. The aim of the invention is to process as high a proportion of plastic recyclates 4 as possible in order to save valuable resources and materials or to reuse them. For this purpose, the device 1 has two extruders 5 and 12 that can be controlled independently of one another, the extruder 5 being used exclusively for processing a granulated pure plastic material 3 and the extruder 12 being used exclusively for processing a likewise granulated plastic recyclate 4. The basic materials 3 and 4 are each introduced into the corresponding inlet 9 of the extruders 5, 12 so that they reach the housing cylinder 7 and are transported and compressed within the extruders 5, 12 by means of the rotatably mounted extruder screws 8. The extruder screws 8 rotate around their axis of rotation at a speed n1 or n2, so that a pressure p1 or p2 is exerted on the basic materials 3 and 4, which leads to heating through friction. In order to be able to control the melting of the basic materials 3, 4 in a targeted manner, heating devices 6 are additionally present on the extruders 5 and 12. For thermal control of the melts, the extruders 5 and 12 also have temperature measuring devices T1 and T2, which together with an electronic processing unit 16 record the prevailing temperatures within the extruders 5, 12 and a enable possible intervention with regard to increasing or reducing the temperatures. In the extruder 5, a melt stream 11 is generated from the pure plastic material 3 and in the extruder 12 from the plastic recyclate 4, which is discharged via the injection nozzles 10 at the ends of the extruders 5, 12. The melt streams 11 from both extruders 5 and 12 then combine within a mixing device 13, thereby creating a common mixed melt stream 14. The extruders are decoupled from one another, which means that the melt streams 11 each pass through a one-way valve 20, so that the melt streams 11 can be individually switched on or shut off. The mixed melt stream 14 is homogenized in a static mixer 19 following the mixing device 13 in the direction of flow. Following this, the mixed melt stream 14 is examined for its composition using a measuring device 15, which in this case is a spectral-optical analysis measuring device. The measurement signal is converted within the electronic processing unit 16 and can be used, for example, to change the speed, pressure and/or temperature within the extruders 5 and 12 or to adjust the mixing ratio between the basic materials 3 and 4 and thereby compensate for undesirable quality deviations in the mixed melt stream 14. The spectral-optical analysis measuring device 15 has a spectrometer 17 in a manner known per se, which is only shown in outline in the figure.

LIST OF REFERENCE SYMBOLS:

1

contraption

2

Plastic part

3

Pure plastic material

4

Plastic recyclate

5

Extruders

6

Heating device

7

Housing cylinder

8th

Extruder screw

9

inlet

10

Spray nozzle

11

Melt flow

12

Extruders

13

Mixing device

14

Mixed melt stream

15

Measuring device

16

electronic processing unit

17

spectrometer

18

Injection molding tool

19

static mixer

20

One-way valve

Claims (15)

Device (1) for producing plastic parts (2) from a mixture of pure plastic material (3) and plastic recyclate (4) as basic materials, comprising a plasticizing unit or an extruder (5), with a housing cylinder (7) equipped with a heating device (6) in which an extruder screw (8) coupled to a drive is rotatably mounted, wherein an inlet (9) serves to feed the basic materials (3, 4) to be processed into the housing cylinder (7) and at the end of the extruder screw (8) there is at least one spray nozzle (10) for discharging a liquid melt stream (11), characterized in that the device (1) has, in addition to the first extruder (5) processing the pure plastic material (3), at least one further extruder (12) used exclusively for processing the plastic recyclate (4). Device according to Claim 1 , characterized in that the extruders (5 and 12) are constructed identically. Device according to one of the preceding claims, characterized in that the melt streams (11) of both extruders (5, 12) are combined in a mixing device (13) to form a mixed melt stream (14). Device according to Claim 1 or 2 , characterized in that both extruders (5, 12) are components of a mixing device (13) in which the melt streams (11) of the extruders (5, 12) are combined to form a mixed melt stream (14). Device according to Claim 3 or 4 , characterized in that, viewed in the flow direction of the melt stream (11), a measuring device (15) for analyzing the properties of the individual melt streams (11) is provided upstream of the mixing device (13). Device according to Claim 3 or 4 , characterized in that in the mixing device (13) or following the mixing device (13) in the flow direction of the melt streams (11), a measuring device (15) for analyzing the properties of the mixed melt stream (14) produced is present. Device according to Claim 6 , characterized in that the measuring device (15) is a spectral-optical analysis measuring device. Device according to Claim 7 , characterized in that the spectral-optical analysis measuring device (15) generates an infrared light or has a laser for generating the light required for the measurement. Device according to Claim 8 , characterized in that the light signal of the measuring device (15) can be processed and evaluated by means of an electronic processing unit (16) and a spectrometer (17). Device according to Claim 9 , characterized in that the measuring device (15) and the electronic processing unit (16) are components of a control system for adjusting the composition of the mixed melt stream (14). Device according to one of the Claims 3 until 10 , characterized in that the device (1) has a static mixer (19) for homogenizing the mixed melt stream (14). Device according to one of the preceding claims, characterized in that the extruders (5, 12) are decoupled from one another, for which purpose the melt streams (11) each pass through a one-way valve (20) so that the melt streams (11) can be individually switched on or shut off. Method for producing plastic parts from a mixture of pure plastic material (3) and plastic recyclate (4) as basic materials, with a device (1) according to one of the preceding claims, characterized by the method steps: - introducing one basic material (3, 4) via the inlet (9) into one of the extruders (5, 12) assigned to the respective basic materials (3, 4), - melting the basic materials (3, 4) to form a pasty or liquid plastic melt stream (11), - combining the individual melt streams (11) of the extruders (5, 12) to form a mixed melt stream (14), - discharging the homogeneous mixed melt stream (14) into a cavity of an injection molding tool (18) having the negative shape of the plastic part (2) to be produced. Procedure according to Claim 13 , characterized in that the mixed melt stream (14) is examined for its composition permanently or at defined time intervals by means of the spectral-optical analysis measuring device (15). Procedure according to Claim 14 , characterized in that depending on the measurement result of the spectral-optical analysis measuring device (15) and by means of a comparison with target values stored in the electronic processing unit (16), with the involvement of the electronic processing unit (16), a control for adjusting the composition of the mixed melt stream (14) is carried out by controlling the individual extruders (5, 12).

Images